This invention relates to a method of making a double base propellant powder (expected classification: Class 264, Subclass 3).
Production of low density double base propellant grains by a continuous globular powder manufacturing process traditionally uses a salt water suspension of discrete particles of a lacquer of nitrocellulose (NC) in ethyl acetate stabilized by addition of diphenylamine to the lacquer. Other solvents and stabilizers could be used so long as the solvent is immiscible in water. That process is described in detail in U.S. Pat. No. 3,679,782, issued July 25, 1972 to Andrew and Halverson entitled "Manufacture of Globular Powder", commonly assigned herewith, which is incorporated by reference herein as if set forth at length. The '782 patent notes the necessity for a dewatering salt to osmotically force out any water in the lacquer.
Prior to the process of the '782 patent, double base propellant was, for 30 years, only made by a batch process substantially as described in U.S. Pat. No. 2,027,114, issued Jan. 7, 1936, where closer control of raw material concentrations is possible. In the continuous process, however, close control of minute concentrations becomes difficult or expensive due to the large volumes of materials and the slow or rapid buildup of materials that can occur because new materials are continuously being added to the process. The level of dewatering salt is one such concentration. If the dewatering salt concentration is 3.5 to 6 percent by weight of the liquor, then control is not so hard and there is enough leeway to allow for minor production errors. However, if the salt concentration must be maintained at a constant very low level (i.e. less than about two tenths of a percent), then production control becomes difficult, especially if this is attempted in equipment which is designed to control to much less precise concentrations. However, since the dewatering salt was necessary to control final grain density, a solution to the problem of how to control dewatering salt concentrations to the levels (0.1%-0.2% by weight) necessary to produce low density (i.e. with a specific gravity of 1.150 to 1.275) base grains by a continuous production process was not obvious and the production of low density base grain by the continuous process was therefore not thought to be practical or economical. A solution to this problem was needed but, despite year after year of research effort, went unrealized.
The solution only came when Olin Corporation, the assignee, hired a young new engineer who addressed the problem without the knowledge that it couldn't be solved. The solution of the present invention was to eliminate the dewatering salt which had been thought to be necessary and to control grain density in other ways (e.g. by compressively rolling the grains).